In recent years, with continuing size reduction of cameras, proximity sensors, direction sensors, acceleration sensors, angular velocity sensors, illuminance sensors, and so forth, these various sensors have been mounted on mobile electronic devices such as smart phones. In electronic devices with liquid crystal panels in particular, an illuminance sensor measures the surrounding brightness, and the brightness of a backlight is adjustable in accordance with the surrounding brightness. The following technology is known to realize illuminance measurement in spectral sensitivity characteristics near luminosity. That is, a plurality of photodiodes with different spectral sensitivity characteristics are provided in an illuminance sensor, and photocurrents of the photodiodes are calculated.
FIG. 24 is a cross sectional view of an optical sensor of the related art. FIG. 25 is a diagram illustrating the spectral sensitivity characteristics of the optical sensor illustrated in FIG. 24. As illustrated in FIG. 24, the optical sensor includes two light receiving elements (PD1 and PD2) with different spectral sensitivities. The light receiving element PD1 and the light receiving element PD2 each have a three-layer structure including a p-type diffusion layer (P+), an n-type well layer (N-Well), and a p-type substrate (P-Sub), and have two photodiodes (PD_vis and PD_ir) having PN junctions. In the light receiving element PD1, the P+ layer and the P-Sub are grounded. In the light receiving element PD2, the P-sub is grounded, and the P+ layer and the N-Well layer are connected to each other.
Accordingly, as illustrated in FIG. 25, the spectral-response characteristic PD_clear (PD_vis+PD_ir) is obtained by the light receiving element PD1, and the spectral-response characteristic PD_ir is obtained by the light receiving element PD2. When PD1 (PD_clear)−PD2 (PD_ir) is calculated, a spectral-response characteristic corresponding to PD_vis is obtained, which is a characteristic whose peak sensitivity is close to luminosity, and accordingly illuminance can be measured.
Watch-type terminals and glasses-type mobile electronic devices have also been put to practical use as sub terminals for smart phones. This provides an environment where a person wearing such a device can monitor his/her biometrics information such as the heart rate and the amount of exercise, which enables the wearer to manage himself/herself. Furthermore, an ultraviolent sensor may be provided in such a mobile electronic device used outdoors. The ultraviolet sensor measures the intensity of ultraviolet rays included in sun light, thereby prompting the user to protect against sunburn or recording the integrated quantity of ultraviolet rays received during day. Accordingly, the use of such a mobile electronic device enables management of the user's health information. It is preferable that the device have the function of detecting, in addition to illuminance, the intensity of light in a certain wavelength range, such as the ultraviolet range.
For example, PTL 1 describes an ultraviolet measurement device with an UV sensor and an illuminance sensor. The ultraviolet measurement device described in PTL 1 determines whether the device is in an environment where ultraviolet measurement is possible, on the basis of the output of the illuminance sensor, and, when it is determined that the environment allows ultraviolet measurement, the ultraviolet radiation dose is measured using the UV sensor. Accordingly, the accurate ultraviolet radiation dose can be measured.
The device described in PTL 1 is for accurately measuring ultraviolet rays. Since a cover member that only allows ultraviolet rays to pass through is provided above the illuminance sensor, the illuminance cannot be accurately measured. To measure the illuminance, a sensor window for the illuminance sensor must be additionally provided.
In a mobile electronic device that has an illuminance sensor and an ultraviolet sensor, an attempt has been made to employ a common sensor window for the ultraviolet sensor and the illuminance sensor in order to improve the design while making the number of optical sensor windows as few as possible.
PTL 2 describes an optical sensor that integrates a visible light sensor and an ultraviolet sensor on one SOI substrate. According to the optical sensor described in PTL 2, the ultraviolet intensity and the illuminance can be measured while reducing the area where the sensors are mounted.